Have CustomInput respect the hidden property

[protocol_1903]

As in title. Currently, when you have the hidden or hidden_in_factoriopedia flag to true, the custom input is not hidden from the controls GUI. This is counterintuitive and means that mods cannot have custom inputs that are not modifiable by the player, and they must always be shown. You can get around this by using linked_game_control but this is unreliable due to players being able to change those controls, and your selection of input sequences is limited.

[Rseding91]

Even if this existed, the player could still modify the binding in the config.ini file outside of the game. What is your use-case for a input that the player can't change?

[protocol_1903]

Detecting arbitrary events that have no direct binding, mostly mouse clicks, to override vanilla GUI interactions